1. Field of the Invention
The invention relates to cable suspensions, and particularly to equipment for rigging cable suspensions.
2. Description of the Related Art
It is generally known to suspend a cable or conductor from a plurality of aligned and spaced apart utility poles to form a power distribution or communication system, or some similar utility transmission system. Typically the utility poles are characterized by a single crossarm which extends horizontally from the utility pole and which supports the cable. In order to isolate the cable from the crossarm the utility transmission system also includes an insulator which is supported by the upper surface of the crossarm at or near the end of the crossarm and which in turn supports the cable. Known insulators are made of porcelain or some other insulative material, are typically generally cylindrical, and are characterized by an annual groove which extends around the insulator. When suspended, the cable rests in the groove in the insulator.
In order to suspend a cable from a utility pole to form a utility transmission system, the cable must be positioned on the crossarm of the utility pole and then placed under tension and drawn to the desired "sag". "Sag" describes the tension of the cable and reflects the magnitude of deflection of the cable as it extends between utility poles. After the cable is placed under sufficient tension so that the cables extend between utility poles with the desired amount of sag, the cable must be positioned into contact with the groove in the insulator on the crossarm. Because of the relatively large weight of the suspended cable and the tension applied to the cable to provide the desired amount of sag, suspending the conductor and positioning the conductor in the groove of the insulator can be difficult.
In the design of utility transmission systems, it is often desirable for the system layout to include a corner, which requires the cable to follow a sharply curved or cornered path. A corner in a typical utility transmission system is accomplished by suspending the cable from a "corner pole". A corner pole is substantially similar to the typical utility pole described above except that a corner pole generally includes a pair of crossarms extending therefrom. As on the standard utility pole, each crossarm on a corner pole supports an insulator on its upper surface adjacent the end of the crossarm.
Placing the conductor or cable under tension on a corner pole and repositioning the cable on the insulators supported by the pair of crossarms can be particularly difficult because, in addition to the weight and axial tension on the conductor, lateral forces act on the cable to "pull" the cable inwardly of the corner as the cable wraps around the insulators. It is because of the lateral forces which "pull" the cable on the corner pole that require the cable to be supported a pair of insulators supported by dual crossarms.
In the prior art, it is known to use various rigging equipment, such as a block, to suspend the cable from the crossarm of a pole while the cable is drawn into tension. It is also known in the prior art to use additional equipment, such as a hoist, to reposition the cable into contact with the grooved insulator. While such known rigging equipment is capable of suspending equipment from utility poles, rigging a utility transmission system can still be difficult. For example, known rigging blocks are mounted on the crossarm inwardly of the insulator with respect to the utility pole to support the cable as tension is applied to the cable to bring the cable to the desired sag. A hoist or some other device must then be used to lift the cable upwardly and outwardly away from the block, over the insulator, and into contact with the groove in the insulator. Such repositioning of the cable can be difficult because the cable may be under tension in excess of 500 pounds of force depending on the weight of the cable, the "sag" of the cable, and the lateral "pull" of the corner, if any. Lifting the cable upwardly and outwardly to reposition the cable subjects the cable to additional tension. Further, it can be difficult to place a cable in contact with the pair of insulators supported by the dual crossarms of a corner pole in a single operation because of the close proximity of the pair of insulators.
It is an object of the invention to provide a stringing block mountable on the crossarm of a utility pole for rigging a cable for suspension from the utility pole.
It is a further object of the invention to provide a stringing block which supports a cable suspended from a utility pole while the cable is under tension and which positions the cable into contact with an insulator.
It is a further object of the invention to provide a stringing block mountable on a corner pole for supporting and positioning a cable under tension on a pair of insulators without the use of any additional, ancillary equipment.
It is among the other specific objects of the invention to provide a stringing block for rigging a cable on a utility pole, and which can be safely and easily removed from the utility pole once the cable is suspended from the utility pole.